In December 2010, St. Jude Medical Inc. issued a warning letter to doctors: Wires inside Riata defibrillator leads—cables that connect the heart to implantable defibrillators—were sometimes breaking through their insulation from the inside out.

The problem, which ultimately led to a recall last year, could cause defibrillators to send unnecessary jolts to the heart or fail to deliver lifesaving shocks to return chaotic heart rhythms back to normal. The company said it had identified dozens of cases with visible signs of the problem, and pulled Riata from the market.

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St. Jude had been tracking the problem for several years, according to company documents collected by the Food and Drug Administration and reviewed by The Wall Street Journal. Cases involving the so-called inside-out abrasion date to at least October 2005, the documents show. Inside-out abrasion became a focus of an internal St. Jude audit, which examined multiple cases of the failure before April 2008.

Read More: The Wall Street Journal

For many doctors, this was the first notice of a problem with Riata.